I have tried the last 3 major releases and they all seem to hickup on Android USB tethering. I tried the clamping and altering MTU. It seems like Chrome may work better than Firefox for some reason. Firefox straight up drops some of the data. I use the exact same setup on a Netgear WNDR4300 and it works as expected.
And the question is.....?
Just some more information. I have a usb2 usbc to usb a cable. When I put a usb 1 hub between the router and the samsung tab a, it does work properly. I can't say what this means but I draw 2 theories. 1) That the problem involves usb somehow 2) That a high rate on input is glitching the system. Again when using rndis_host and a direct connection, the connection is almost unusable and drops out. There are no usb errors in the dmesg btw.